Alkaline earth aluminate phosphors are known and are available commercially. For example, strontium aluminate phosphors activated with europium emit in the green region of the spectrum. These phosphors are long persistence phosphors which are highly desirable. However, their luminescence disappears after exposure of the phosphor to moisture. Hydrolysis of the phosphor begins after only a few minutes of exposure to moisture, as determined by an increase in pH from about 6 to about 11. The solid phosphor powders also begin to coalesce to form aggregates or even a hard block of cement-like material that is no longer useful. Phosphorescence decreases more slowly, but the phosphor emission becomes very dim after a few hours.
This sensitivity to moisture severely limits the utility of the phosphor, which must be kept away from moisture, as by formulating in a nonaqueous medium.
Other inorganic materials are known to be sensitive to moisture, such as calcium aluminate, barium aluminate, strontium sulfide, calcium sulfide, barium silicate, (CaSrBa) thioaluminate, strontium thiosulfate and the like.
Thus an effective method of protecting each of such inorganic material from moisture would be highly desirable.